The field of the invention relates generally to processes for the preparation of higher alcohols from lower alcohols by Guerbet condensation.
Ethanol is the major liquid biofuel manufactured worldwide. However, there are still many problems associated with the use of ethanol fuel in internal combustion engines, including its water solubility, corrosivity and the differences in its fuel properties compared to gasoline. In order to overcome the disadvantages of ethanol as a fuel, catalytic condensation of lower alcohols (e.g., ethanol) to higher alcohols (e.g., n-butanol) can be carried out. Compared to ethanol, n-butanol has several advantages. For instance, n-butanol can be burned in the existing gasoline engines without practically any engine or car modifications and it has higher energy content and air-to-fuel ratio. Thus n-butanol an excellent green replacement for gasoline.
n-butanol can be obtained by means of the well-known Guerbet reaction, which makes it possible to catalytically convert a low-molecular-weight alcohol (e.g. ethanol) into a linear or branched alcohol with a higher molecular weight. The main disadvantages associated with the Guerbet reaction are the production of water, which must be eliminated from the reaction medium in order to favor the formation of the desired compounds; the production of side products including aldehydes, non-target alcohols, and carboxylic acids; and limited selectivity to n-butanol, limited ethanol conversion, and concomitant low butanol yield.
A need therefore exists for improved processes for the generation of higher alcohols by Guerbet condensation of lower alcohols.